Q1: What is the starting base diameter of your (lead) bullets before loading? (How does that compare to the diameter of jacketed rounds?)

Q2: What is the resulting diameter of your cases at the mouth of your loaded (lead) rounds?
It should nominally be 0.420-0.423", or whatever minimum drops the cartridge into the
barrel with a satisfying "plunk" when it stops.

Use the taper crimp until it will seat all the way against the chamber stop by gravity alone.